This application is related to a non provisional patent application filed on the same date as the date of filing of this application, such related application being entitled xe2x80x9cSplit Mechanical Face Sealxe2x80x9d naming as inventors Fred Pippert and John Nunn, and assigned to the same assignee as that of the present application.
1. Field of the Invention
The present invention relates generally to the field of seals employed to effect a seal between a housing and a rotatable shaft extending from the housing. More particularly, the present invention relates to a method and apparatus for optimizing the sealing engagement between a split mechanical seal and a rotatable shaft.
2. Setting of the Invention
Many mechanical devices employ a rotatable shaft that extends from a housing containing structural devices immersed in, or contained within, liquids, gases and other materials. Examples are crankshafts extending from internal combustion engines, drive shafts extending from inboard motors to propellers, and process machinery in which blades or other rotating devices rotate within a mixing chamber. It is usually necessary to provide a seal between the shaft and housing of these devices to permit rotation of the shaft while simultaneously preventing the escape of materials contained within the housing.
Replacement or repair of the shaft seals is preferably done without disassembling the equipment secured to either end of the shaft. Split mechanical face seals are commonly employed for this purpose. The replacement seal is constructed in two parts that can be assembled around the shaft to replace the faulty seal. The normal procedure for applying a split mechanical seal to a shaft is to place each half of the seal around the shaft and bolt the two seal halves together. The replacement seal is then bolted to the housing to complete the seal between the housing and the shaft.
Split mechanical seals often include a large number of component parts which, to properly seal with the shaft, must align precisely when the two seal halves are brought together and bolted to each other. A common technique for facilitating the assembly of the two seal halves around a shaft is to employ one or more alignment pins that project rigidly from one seal half into a recess formed in the mating part of the other seal half The alignment pins maintain axial alignment between the two halves as they are bolted together about the shaft.
Prior art arrangements for assembling the two halves of a split mechanical seal using alignment pins can prevent optimum sealing contact and optimum gripping between the mechanical seal and the shaft. The problem arises from the fact that the rigid alignment pin in one seal half does not precisely align axially with the recess in the mating seal half until the two halves are brought fully together to their design contact position about the shaft.
Before the two seal halves are brought fully together, the pin axis and the conventional circular recess axis are non coaxial. The recess dimensions in most prior art split seal designs are only marginally larger than the alignment pin dimensions. As a result, the alignment pin resists entering the alignment recess during the placement of the seal assembly about the shaft. Even after the alignment pin enters the receiving recess on the mating seal half, the misalignment of the axis of the alignment pin and that of the recess resist the tightening force imposed by the bolts clamping the two seal halves together. Resistance to tightening of the bolts can mistakenly be interpreted as complete and proper engagement of the two seal components which is required to obtain the maximum gripping force with the shaft and to form an optimum seal between the seal halves and the shaft.
It is understood that the binding problem associated with the movement of the alignment pin through the mating recess can be reduced by increasing the diameter of the recess, however, merely enlarging the recess diameter permits axial displacement between the two seal halves as they are being assembled. Axial alignment between the two seal halves as they are being bolted together is critical in ensuring an effective seal between the shaft and the housing and in obtaining a secure grip on the shaft.
From the foregoing it may be appreciated that a primary object of the present invention is to provide an alignment method and apparatus that permits axial alignment between the two mating halves of a split mechanical seal that is effective during the initial and final placement of the seal about a shaft.
Another object of the present invention is to provide an alignment arrangement in a split mechanical seal that allows the two components of the seal to freely move radially toward each other while maintaining a fixed relative axial position between the two halves.
A related object of the present invention is to provide a low-cost, efficient apparatus and method for assembling a split mechanical seal about a shaft whereby the two components of the seal may be secured to each other in a position achieving an optimum seal with the shaft.
An important object of the present invention is to provide an alignment technique in which the alignment pin of one part of a split mechanical seal can be quickly and easily aligned with a mating recess in the second part of the seal without requiring axial alignment between the pin and recess.
The alignment recesses in one half of a split mechanical seal are provided with circumferentially extending, linear sidewalls that closely engage the sides of an alignment pin extending rigidly from a second-half of the mechanical seal. The alignment pin is free to move radially within the recess between the linear sidewalls as the two halves of the split seal close radially together. The contact between the sides of the alignment pin and the sidewalls of the recess at the final closing point ensures a fixed, correct axial relationship between the two halves of the seal.
The provision of an alignment recess that permits radial movement and limits axial movement facilitates the assembly of the two split halves about a shaft. The initial entry of the end of the alignment pin into the recess is simplified as compared with the prior art technique requiring precise alignment of the pin with the recess before closing radial movement between the two seal halves could be achieved.
The alignment method and apparatus of the present invention prevents the faulty assembly of split mechanical seals about a shaft caused by the binding encountered in conventional alignment systems.
The described features, objects and advantages of the present invention will be more filly understood and better appreciated by reference to the following drawings, specification and claims.